Motor control device and printer device

Abstract

Speed fluctuations are decreased with a simple method even when a stepping motor ( 100 ) having comparatively large torque fluctuations is used. A drive pulse modulating unit ( 112 ) which modulates the frequency of a drive pulse to be inputted to the stepping motor ( 100 ) is provided. The drive pulse modulating unit ( 112 ) modulates the constant frequency of the drive pulse such that the frequency of the drive pulse within excitation-phase one cycle of the stepping motor ( 100 ) is: low for a period that is, by ⅛ cycle of the excitation-phase one cycle, before an excitation phase where the vibration of the stepping motor is the maximum; and high in an excitation phase that is by ½ cycle subsequent to the excitation phase where the drive pulse frequency is low.

The invention claimed is: 
     
       1. A motor control device to control a stepping motor that performs driving by taking as input a drive pulse having a constant frequency, the motor control device comprising:
 a drive pulse modulator to modulate a frequency of a drive pulse to be inputted to the stepping motor, 
 the drive pulse modulator modulating the frequency of the drive pulse having the constant frequency such that the frequency of the drive pulse within excitation-phase one cycle of the stepping motor is: lower than the constant frequency for a period that is, by ⅛ cycle of the excitation-phase one cycle, before an excitation phase where vibration of the stepping motor is the maximum; and higher than the constant frequency in an excitation phase that is by ½ cycle subsequent to the excitation phase where the drive pulse frequency is lower than the constant frequency. 
 
     
     
       2. The motor control device according to  claim 1 ,
 wherein the drive pulse modulator performs modulation such that the frequency of the drive pulse within the excitation-phase one cycle of the stepping motor takes: a minimum value of the excitation-phase one cycle, for a period that is, by ⅛ cycle of the excitation-phase one cycle, before the excitation phase where the vibration of the stepping motor is the maximum; and a maximum value of the excitation-phase one cycle, in an excitation phase that is by ½ cycle subsequent to the excitation phase where the vibration of the stepping motor is the maximum. 
 
     
     
       3. The motor control device according to  claim 2 ,
 wherein the drive pulse modulator performs modulation such that an average value of the maximum value and the minimum value is the same the constant frequency. 
 
     
     
       4. The motor control device according to  claim 1 ,
 wherein the drive pulse modulator performs modulation such that a change in frequency of the drive pulse within the excitation-phase one cycle of after modulation forms a sine wave. 
 
     
     
       5. A printer device that prints on recording paper, the printer device comprising: the motor control device according to  claim 1 ; and a stepping motor controlled by the motor control device, as a convey driving source for the recording paper. 
     
     
       6. The printer device according to  claim 5 ,
 wherein the drive pulse modulator modulates the constant frequency only in a print operation of printing on the recording paper. 
 
     
     
       7. The printer device according to  claim 5 ,
 wherein the motor control device comprises a modulation count setter which sets a maximum modulation count of the frequency of the drive pulse based on a print unevenness level, covering the excitation-phase one cycle of the stepping motor, of a print result obtained by printing on the recording paper. 
 
     
     
       8. The printer device according to  claim 7 ,
 wherein the modulation count setter outputs a motor exchange notice notifying exchange of the stepping motor when the maximum modulation count exceeds a threshold value.